Ozone is used for various industrial applications, for example, as an oxidizing agent and as a bactericide. One major application for ozone is in purifying potable water. Another application is in the treatment of sewage. Still another exemplary application is to oxidize volatile organic compounds (VOC's) in air. In addition to industrial applications, ozone has been used for treating residential swimming pools to reduce the need for chemicals such as chlorine and has been used for medical purposes. Ozone also has been used to treat pond water, for example, in zoo ponds for hippos and in fish farm ponds.
One type of ozone generator uses high voltage corona discharges to convert a portion of the oxygen in a feed gas to ozone. Another type of ozone generator uses high intensity light to convert oxygen to ozone. Either air or, preferably, a gas containing a high concentration of oxygen is fed to the ozone generator and a portion of the oxygen in the feed gas is converted to ozone. A high concentration oxygen output from an oxygen concentrator, for example, may be used to supply the feed gas for an ozone generator. An oxygen concentrator removes nitrogen from air and typically produces about 92% to 95% pure oxygen, with the remainder being primarily argon. When air is used as the feed gas, a typical ozone generator may produce a gas having up to about 1% ozone concentration. When 92% to 95% concentration oxygen from an oxygen concentrator is used as the feed gas, a typical ozone generator may produce up to about 5% ozone concentration. With an extremely high efficiency ozone generator, the output may have up to about 20% ozone concentration. However, the amount of ozone in the output from an ozone generator may decrease over a period of time, primarily due to a declining efficiency of the oxygen concentrator in providing a constant feed stock.
It should be appreciated that when air or an oxygen rich gas is supplied to an ozone generator, the same quantity of gas will be discharged from the ozone generator, whether or not the ozone generator is working properly. It is often desirable to know if the ozone generator is working properly, especially when the ozone is used for purification of potable waters. In order to monitor the composition of the output gas from an ozone generator, it is necessary to have an ozone monitor or ozone level sensor. In the past, only a few ozone monitors have been available and they have tended to be expensive and inaccurate.
It is known in the art that the concentration of oxygen in gas can be determined from the temperature of the gas and the speed that a high frequency sound pulse travels through the gas. U.S. Pat. No. 5,247,826 discloses a gas concentration sensor in which two piezoelectric transducers are connected together through a coiled tube. Oxygen containing gas from an oxygen concentrator, for example, is passed over one transducer, through the tube and over the other transducer. A thermistor is located at the center of the tube for measuring the average temperature of the gas as it flows through the tube. Periodically, one of the transducers is pulsed and the time required for a sound wave to travel to the other transducer is measured. It will be appreciated that the time will be influenced by the direction that the pulse travels relative to the direction of the gas flow through the tube. In order to eliminate the influence of the gas flow, the two transducers are alternately used for sending and receiving pulses. The pulse travel times both in the direction of the gas flow and against the gas flow are used to determine the oxygen concentration. The coiled tube is used between the transducers to increase the time that it takes for a sound pulse to travel between the transducers, thus increasing the accuracy of the measurement. A direct reading approach is used for determining oxygen level. In other words, the output of the oxygen concentrator is not compared with a reference gas having a known oxygen level. The gas concentration sensor disclosed in this patent has not been used for measuring the concentration of ozone from an ozone generator.